It would have been cool if Barkley showed up at some point to meet Sprocket and Rowlf (not that Sprocket and Rowlf's meeting wasn't cool enough).

Some others:
Bif and Sully meet Beauregard (or anyone for that matter)
Red and Scooter (Just because Red reminds me of MB Skeeter)
Animal and Frazzle (I know, I know, Frazzle wasn't there. But he could have been.)
Sam and the Fraggles
(Sam: You live in a rock?
Gobo: Well, yeah.
Sam: And you've never heard of the Muppets?
Wembley: Well, no.
Sam: Tell me something...are you decent Americans?
Mokey: Well, we don't know what an "American" is, but we are decent.
Sam: Decent, impressionable young minds. There's so much to teach you. Take me with you.
Boober: You scare me!)

Hmm, that's a thught. Sam didn't have much to do in this movie, did he?

Maybe he could have talked to Doc back when Doc was trying to make something of the wierdnes around him.

Sam: And what is a decent American like you, doing at a party like this.
Doc: Well, I was hoping for a nice, quiet...
Sam: THings are never quiet here with these, werdoes, quick pack your bags, you may yet escape them.

Hmm, that's a thught. Sam didn't have much to do in this movie, did he?

Maybe he could have talked to Doc back when Doc was trying to make something of the wierdnes around him.

Sam: And what is a decent American like you, doing at a party like this.
Doc: Well, I was hoping for a nice, quiet...
Sam: THings are never quiet here with these, werdoes, quick pack your bags, you may yet escape them.